In English that person would probably be described as a 'friend'. You can add words to 'friend' to further indicate their closeness to you, best friend, close friend, good friend, friend from work, a friend of mine, friend from X place etc... This topic has come up before, native speakers of English are less strict with their use of this word than speakers of other languages. 'Companion' is normally for romantic partners. 'Mate' suggests you are quite good friends. Again, not what you're looking for.

If you are talking about someone you know from work or school you can call them an "associate", "contact" or "colleague". This would be a normal conversation. "Is he a friend?" "No, he is just an associate from work" An "associate" is someone you see often, more than you would an "acquaintance", but you are not friends. Hope this helps

how about "companion"?

Mate, Companion...